1. Field of the Invention
This invention pertains to a ring laser gyro with a dither spring within a laser block. Particularly, this invention pertains to a dither spring structure and method of suspending a laser block which minimizes thermally induced stress effects on the laser block.
2. The Prior Art
The need for dither of a ring laser gyro is well known and the prior art provides a variety of gyro block suspension structures enabling dither of the block about a generally centrally located axis within a laser path in the block. The prior art dithered ring laser gyros are sensitive to temperature change because of different rates of thermal expansion of the gyro block and the dither spring fastened to the block. Differences in thermal expansion of the spring and the block impart stress onto the block and degrade the accuracy of output from the gyro.
Attempts have been made to solve the problem of different rates of thermal expansion of the dither spring and the block.
One attempt was an exotic alloy dither spring that was economically not viable.
An effort has been made to isolate the effects of different thermal expansion of a mounting platform and the gyro block by interposing a viscous fluid frictional coupling in the gyro suspension. The fluid coupling allows different radial expansion between parallel and generally plate shaped block and dither drive components of the gyro. This effort is documented in U.S. Pat. No. 4,321,557, issued to McNair.
A more relevant example of the prior art efforts at solving the problem is the provision of a gyro block having a central bore and dither spring having a plurality of discrete arcuate segments fastened in a predetermined angular position to the bore within the block. Each individual discrete arcuate segment is suspended by a pair of radial webs which extend radially outward from a central mounting structure, like opposite sides of a piece of pie, to adjoin to the arcuate segment. Each web has a knee type central portion of relatively thin section that probably enables flexure of the web in an attempt to maintain something approximating a constant length during thermal changes. The arcuate segments are discrete and individual from each other and may easily have different natural frequencies from each other which can impart spurious hoop as well as radial stress onto the gyro block during dither. The geometry of this arcuately segmented dither spring is relatively complicated and requires the provision and usage of guide holes for EDM electrodes during fabrication of the spring. From visual examination, it looks like this particular device emphasizes "more evenly distributed forces" directed from an expanding hinge to the gyroscope body. This "evenly distributed force" is attained by a plurality of mounting segments that correspond in number to the quantity of apexes in the gyro body block and selectively arranging contact and location between the hinge segments and the body bore.
It is, therefore, among the objects of the present invention to provide a ring laser gyro with thermal neutrality, a ring laser gyro having an improved gyro dither spring for providing thermal neutrality to a ring laser gyro, and a method of suspending a laser ring gyro body providing improved thermal neutrality. It is the object of the invention to provide a dither spring in which thermally induced dimensional changes in the dither spring are absorbed which thereby minimizes stress on a laser block. These objects are achieved by provision and use of a dither spring having an outer ring member with outer surface segments having mounting surfaces securable to a gyro block bore and generally T-shaped junctions in between the outer surface segments and spaced inward from the major diameter and in non-contact with the gyro block bore, and with radial members extending inwardly from each junction to a central mounting structure for mounting the dither spring to a support.